Platelet-derived Growth Factor (PDGF) is a potent mitogen for a variety of cell types including vascular smooth muscle cells (VSMC). Abnormal growth of VSMC is a component of a number of disease states, such as atherosclerosis, hypertension and neoplasia, that arise with increased frequency in more aged animals. PDGF has been implicated in the development and maintenance of these disease states. PDGF elicits biological activity through three different PDGF isoforms and two distinct receptor types. The mechanisms, however, by which PDGF binding is transduced into biological signals are not clear. In this proposal, the hypothesis that different PDGF-receptor types utilize distinct pathways to elicit alterations in Ca2+i will be tested. Using Multiparameter Digitized Video Microscopy (MDVM) which allows real time observation of alterations in Ca2+i t the level of the single intact cell, the nature of the Ca2+i responses elicited by specific PDGF receptor types, in terms of amplitude, kinetics and location, will be evaluated. These studies will be repeated under conditions in which PDGF-induced alterations in Ca2+i are temporally and spatially modulated through the use of Ca2+ agonists and antagonists (including caged compounds that release Ca2+ and other second messengers upon photolysis). This information will be used to test the further hypothesis that age- dependent changes in the amount, distribution, and/or functional state of the two types of PDGF receptors present in a given cell population are related to changes in PDGF-induced Ca2+i-signalling characteristics observed in cells of different ages. The potential for PDGF-isoform- specific regulation of the growth and differentiation states of VSMC will be evaluated by simultaneously monitoring Ca2+i alterations, the levels of PDGF-receptor proteins and gene expression, and the expression of differentiation-state-specific genes in single cells of differing ages. These studies will document age-dependent alterations in Ca2+ metabolism associated with growth factor signal transduction in VSMC, and will determine whether these age-related changes are due to: 1) altered PDGF- receptor phenotype; 2) a change in the sensitivity of specific receptor types to activation by PDGF isoforms; and/or 3) a change in the responsiveness of certain second messenger systems to specific PDGF- receptor activation. The proposed studies will supply new information regarding the identification of distinct cellular mechanisms for the regulation of normal cell growth and proliferation through the different PDGF receptor types and the role that changes in receptor signaling play in processes that involve aberrant regulation of cell proliferation, such as those associated with aging and cellular senescence.